The present invention relates to a centrifugal drier comprising a rotary cylindrical screening basket and operated cyclically in successive, repetitive cycles in the course of which a product to be dried is charged into the basket under control of a device which interrupts the feeding of the product into the basket when the layer of the product on the cylindrical wall of the rotating basket has reached a predetermined thickness, the product is then partially dried initially as the basket rotates and particulate solid material contained in the product is retained on the basket wall while liquid is centrifugally separated from the product, the partially dried product is washed with a washing liquid projected by an array of orifices or atomizing nozzles disposed in the interior of the basket, and the washed product is finally completely dried, discharged from the basket and removed. Such centrifugal driers have been used in the sugar industry for separating sugar crystals (the particulate solid material) from massecuite (product to be dried).
Each operating cycle of such centrifugal driers is defined by a certain number of parameters, such as acceleration and deceleration of the basket rotation, as well as timing, etc. At the present time, each operating parameter is entered separately into the computer which automatically operates the drier, either by the manufacturer or by the operator, and these parameters are then adjusted empirically on the basis of the operating experience.
In present centrifugal drier installations, certain parameters, such as the time available for each cycle and the volume of the washing liquid utilized, are functions of the charge in the basket. Since it is difficult to measure this charge, one has attempted to maintain the same constant and equal to a predetermined optimum value. For this purpose, it has been proposed to arrange a sensor in the interior of the basket to sense and measure the thickness of the layer of the charged product, which is forced against the cylindrical wall of the basket during rotation thereof, due to the generated centrifugal force. When the sensed layer thickness has reached a predetermined control value, the valve through which the product is charged into the basket is closed. For various reasons, particularly because the product to be dried is not distributed uniformly over the entire height of the cylindrical basket wall during the charging of the basket, the layer thickness measured by the sensor continues to increase for a certain time even after the valve has been closed. The final maximum thickness of the layer exceeds the control value, and the difference therebetween varies according to the properties of the product. Therefore, the same control value causing the valve to be closed and charging of the product into the basket to be discontinued may produce different charges in the successive operating cycles.